Electrochemical energy conversion technologies will come to dominate many aspects of how we produce and use energy over the coming decades. This includes the conversion of fuels, such as hydrogen, methane, and alcohol, directly to electrical energy without the need of a combustion engine. It also includes the creation of useful fuels, other chemicals, and refined metals from electrical energy—processes such as electrolytic hydrogen/oxygen production, chlor-alkali, carbon sequestration, and aluminum refining.
Most of these electrochemical technologies rely on the basic structure developed over a century ago—that is an anode and cathode on opposing sides, with an electrolyte in-between. The electrolyte is most often a solid or liquid that is highly electronically insulating, but facilitates ion transfer between the anode and cathode. This design has proven relatively robust for various systems to this point due to high theoretical energy conversion efficiencies and modularity.
From a design standpoint, though, there are a numerous limitations that prevent these devices from operating to their fullest potential. The first limitation relates to the interface between the electronic conducting material, ionic conducting material, reactants, and products. In fuel cells, as an example, this is manifested in the three phase boundary region—where electron, ion, and reactant/product meet. This region often occurs at the catalyst, which is needed to facilitate the reaction. In a modern proton-exchange membrane fuel cell, only about ⅓ of the catalyst can be used for this reason, as the other ⅔ will not have access to a least one of the three necessary components. To surmount theses issues, high surface area nanocatalysts and supports have been developed along with along with composite electrode formulations incorporating additional electrolyte to extend the reaction zone—but these fixes are not ideal or very often insufficient.
The second limitation relates to mass transport of reactants and products. The reactants and products must compete in the same volume of space—one into the device and one out of the device.